高功率可见光至近红外波段超连续谱光源研究进展

Research Progress of High-Power Visible to Near-Infrared Supercontinuum Source

高功率可见光至近红外波段的超连续谱光源在光电对抗、光学相干层析成像和高光谱激光雷达等方面具有广泛的应用前景。最近几年,涌现了一些用于产生高功率超连续谱光源的新方法,推动了高功率超连续谱光源的进一步发展。本文从主振荡功率放大结构、随机光纤激光器结构以及多路非相干合成这三种用于高功率超连续谱产生的主流方案出发,着重介绍了近年来有代表性的高功率可见光至近红外波段超连续谱光源的研究进展,并综合分析了这三种方案的优缺点以及未来的发展潜力。

Significance Supercontinuum(SC)has experienced a boom in recent decades because of its rich spectral compositions and laser characteristics.At present,the studies of SC mainly focus on power scaling,spectrum extension,and spectrum flatness improvement,among which power scaling enables abundant potential applications,such as photoelectric countermeasures,optical coherence tomography,and hyperspectral lidars.In the photoelectric countermeasure system,a high-power broadband source is employed to suppress and disturb enemy equipment.For example,the AN/AAQ-24(V)directional infrared countermeasure system jointly developed by the United States and Britain has the function of laser jamming,and the corresponding jamming range covers the entire nearinfrared waveband.In the equipment of optical coherence tomography,the material sample is scanned by a broadband source,thus achieving the reconstruction of its two-dimensional or three-dimensional image.Scanning resolution,speed,and sensitivity are three key performance parameters in this equipment,in which the scanning sensitivity can be improved by a high-power source,and the axial resolution can be enhanced by a broadband source.With these factors considered,a high-power SC source is an appropriate choice.In the hyperspectral lidar system,the active hyperspectral detection covering broadband wavelength is attractive in long-range target identification.It has been reported that the active hyperspectral detection of diffusion target has a measurement range of several hundred meters and requires the utilization of quite expensive instruments to produce and detect infrared laser radiation.The laser power is one of the main factors to determine the measurement range limit in this system.The high-power SC source has great application prospects in remote hyperspectral sensing and lidar performance enhancement due to its unique characteristics,such as good direction,broadband wavelength range,and high spectral intensity.Progress We review three major schemes generating high-power visible to near-infrared SC on the main oscillating power amplification(MOPA)structure,random fiber laser structure,and multichannel incoherent combination.Specifically,in the MOPA structure scheme,there are two SC generation schemes according to the generated waveband.One is adopting a MOPA structure combined with a photonic crystal fiber(PCF)or a graded-index multimode fiber(GRINMMF)to achieve a visible SC output.Some typical PCFs for high-power SC generation are also introduced(Fig.2).The other is that the near-infrared SC generates directly from a fiber amplifier.For the SC generation scheme in a random fiber laser,several typically experimental structures are reviewed in detail.In the multichannel incoherent combination scheme,the broadband power combinations of visible SC and near-infrared SC are listed respectively.The advantages and disadvantages of these schemes and their future development potential are comprehensively analyzed.Conclusions and Prospects The visible SC output power reaches 300 W based on the MOPA structure scheme,the near-infrared SC output power has reached 3 kW based on the scheme of random fiber laser,and the emergence of new fibers and schemes brings new energy for the development of high-power SC sources.In terms of high-power visible SC,PCF is the main nonlinear medium and the corresponding studies focus on its structure design.However,the mode field diameter of PCF is small,which means it has less potential for further SC output power scaling.With the further development of the GRINMMF,this fiber with a large core size,beam selfcleaning effect,and unique mechanism of short-wave expansion can promote the further development of high-power visible SC.At present,the generated SC spectral properties of GRINMMF are poor compared with those of PCF.Believing in the future that the SC output power and spectral performance based on GRINMMF can be further improved by optimizing the refractive index curve,doping concentration,and fiber structure.In addition,most of the reported high-power visible SC is achieved by the MOPA structure scheme,and the scheme of multichannel incoherent combination can also scale the visible SC output power effectively,which can be further improved by optimizing the design of the broadband power combiner in the future.For high-power near-infrared SC,the MOPA structure scheme is complex,but it can provide high pump peak power under the premise of ensuring the average pump power,and the generated spectral performance of SC is excellent.For the scheme of the random fiber laser,the generated SC structure is simple with high obtained SC output power,which also needs to achieve more development theoretically and experimentally in the future.The scheme of multichannel incoherent combination has the potential to break the limit of SC output power in the single fiber,but the current development is relatively slow due to the small market demand at home and abroad.However,when the output SC power of the single fiber is close to the limit in the future,the scheme will show its advantages.We select some representative studies of high-power visible to near-infrared SC at home and abroad in terms of the above three schemes and focus on demonstrating the research progress of the National University of Defense Technology in recent years.With the improvement in the fiber drawing technology and semiconductor laser output power,and the gradual application of SC sources in photoelectric countermeasures,optical coherence tomography,and hyperspectral lidars,high-power SC sources can be further developed.